Yellowstone National Park is one of the world's truly extraordinary places. Its landscape, dominated by a great volcanic caldera and sculpted over millennia by water and glacial ice, is host to a dramatically complex flora and fauna. But there is more to Yellowstone's wonders than meets the eye. A nearly unexplored world awaits the curious in the park's streams and lakes, wetlands and beaver ponds, hot springs and geysers. This is the world of microbes--the...